The focus of this program project has been the analysis of mechanisms leading to therapy-related acute myeloid leukemia (t-AML) in patients who previously received a variety of chemotherapeutic agents and/or radiation. Initially we focussed on mapping genes on the long are of chromosome 5 (5q) because deletions of 5q are one of the most common abnormalities in t-AML following treatment with alkylating agents and/or radiation and we defined a 2 to 4 mega base segment on 5q31 as the critical region. Loss of chromosome 7 is the most common change in t- AML; we have mapped two loci on 7q (7q22 and 7q32-33) as containing the critical genes. We will define the critical regions on chromosomes 5 and 7 more precisely and search for the involved genes. Drugs that target topoisomerase II are sometime associated in t-AML with balanced translocations especially involving the MLL gene at 11q23. We are analyzing the structure of MLL and the sequence of the MLL genomic breakpoints to search for potential mechanisms for breakage and translocation of MLL following exposure to the epipodophyllotoxins. We will analyze the cellular localization, phosphorylation state and the binding potential of the most common MLL partner gene, namely AF4 (4q21).